A backlight used for a liquid crystal display for example is composed of a light guide plate, a discharge lamp device or the like and the discharge lamp device is composed of a light source device and a reflection member. A conventional light source device is structured such that an end of an opening of a glass bulb in which a fluorescent material layer is layered on an inner periphery is sealed with electrodes via a bead glass. In the glass bulb, mixed gas of neon and argon and mercury are diffused and filled in an appropriate amount, respectively. This light source device works in a manner as described below. Specifically, when a voltage is applied between the electrodes to ionize and excite the mixed gas and mercury in the glass bulb, ultraviolet is generated. This ultraviolet is converted to visible light by the fluorescent material layer. This visible light passes through the glass bulb and is emitted to outside, thereby providing light emission.
However, the above light source device using mercury is highly dependent on a temperature and thus has a poor luminous flux startup characteristic at a low temperature and is not desirable from a viewpoint of environmental protection. Thus, such a light source device that does not use mercury has been desired.
In view of the above, such a light source device that uses noble gas instead of mercury has been disclosed by Japanese Patent Unexamined Publication No. H5-29085, Japanese Patent Unexamined Publication No. H10-112290, and Japanese Patent Unexamined Publication No. 2001-325919.
A light source device disclosed by Japanese Patent Unexamined Publication No. H5-29085 has a structure as described below. Specifically, a fluorescent material layer is formed on an inner circumference face of a glass bulb in which both end sections are sealed. This glass bulb is filled with inert gas consisting of xenon or mainly including xenon. One end section of the glass bulb includes an inner electrode and almost the entire length of an outer face of the glass bulb is joined with an outer electrode having a stripe shape. The inner electrode and the outer electrode of the light source device as described above are connected with a high-frequency lighting circuit to which a high-frequency voltage is applied. This high-frequency lighting circuit is designed so that an effective value of current flowing from the inner electrode to the outer electrode is smaller than an effective value of current flowing from the outer electrode to the inner electrode to reduce a rate at which noble gas ion is implanted to a glass wall of the glass bulb so that the noble gas is prevented from being lost.
A light source device disclosed by Japanese Patent Unexamined Publication No. H10-112290 has a structure as described below. A glass bulb filled with noble gas such as xenon have both end sections at which inner electrodes having an identical polarity are provided. An outer circumference face of the glass bulb is wound with a linear outer electrode whose polarity is different from that of the inner electrodes. This light source device emits ultraviolet that reacts with light oxygen in air existing around the light to generate ionized gas molecules having an bacteriostatic action (e.g., ozone).
Furthermore, a light source device disclosed by Japanese Patent Unexamined Publication No. 2001-325919 has a structure as described below. A long and thin and translucent airtight container is provided in which both end sections of a glass bulb are sealed so that the interior works as a discharge space. This airtight container is filled with discharge medium mainly including noble gas and is sealed to include therein one or a plurality of inner electrode(s). An outer surface of the glass bulb is almost in contact with an outer electrode and the outer electrode and the discharge space have therebetween a capacitance change means. The capacitance change means changes the distribution of impedance between the outer electrode and the discharge space so that uniformly or desirably changed light intensity distribution can be obtained along the longitudinal direction of the airtight container.
However, the light source devices introduced by the above publications find difficulty in completely sealing an outer electrode to a glass bulb and thus a small space is caused. The status as described above not only causes a light source device to emit light in a very unstable manner but also causes air in this small space to induce dielectric breakdown. This causes a problem where ionized gas molecules (e.g., ozone) for example break the outer electrode or the glass bulb.
Furthermore, even when the light source devices introduced by the above publications are manufactured so that a clearance is prevented from being caused between an outer electrode and a glass bulb by mechanically abutting the outer electrode to the glass bulb or by adhesive agent, an evaporation method, or a sputter technique, the adhesion status therebetween is unstable due to a manufacturing error, vibration during the operation, or an environmental change (e.g., temperature change) for example. As a result, a space is partially caused therebetween.
In view of the above, it is an objective of the present invention to provide a discharge lamp device including such a light source device that prevents ozone for example from being caused between an airtight container filled with noble gas and an outer electrode to prevent dielectric breakdown and that includes a reflective surface.